A Point-Source Survey of M31 with the Spitzer Space Telescope

We explore the stellar population of M31 in a Spitzer Space Telescope
survey utilizing IRAC and MIPS observations. Red supergiants are the
brightest objects seen in the infrared; they are a prominent
evolutionary phase. Due to their circumstellar envelopes, many of these
radiate the bulk of their luminosity at IRAC wavelengths and do not
stand out in the near-infrared or optically. Going fainter, we see large
numbers of luminous asymptotic giant branch stars (AGB), many of which
are known long-period variables. Relative to M33 the AGB carbon star
population of M31 appears sparse, but this needs to be spectroscopically
confirmed.